The invention relates to a synchronizing device.
Synchronizing devices for selector transmissions of motor vehicles have a sliding sleeve non-rotatably connectable with a shaft by axial displacement and having an inner tooth, a clutch body provided with an outer tooth and a synchronizer ring which in peripheral direction has a form-locking connection with the sliding sleeve via an outer tooth and a frictional-engagement connection with the clutch body. The teeth of the synchronizer ring has blocking surfaces which are disposed relative to each other forming an angle for engaging corresponding blocking surfaces of the teeth of the sliding sleeve.
Such synchronizing devices are widely known and have been described, for example, in German Patent 26 59 448. If a gear is activated by moving the sliding sleeve in axial direction out of the neutral position, the sliding sleeve takes along the synchronizer ring pressing it against an opposed cone of the clutch body. Hereby is produced a frictional-engagement connection between synchronizer ring and clutch body whereby a rotational speed adaptation is obtained between the shaft, the sliding sleeve and the synchronizer ring, the same as between the clutch body and the appertaining gearwheel of the wheel pair to be engaged. Blocking surfaces provided on the synchronizer ring are at the same time brought to a position in which they attain engagement with appertaining and adapted blocking surfaces on the sliding sleeve and thereby prevent an axial displacement of the sliding sleeve in direction to the clutch body. The blocking surfaces are usually fitted on an outer tooth of the synchronizer ring adapted to the outer tooth of the clutch body; the mating surfaces are here mounted on the ends of the teeth which form the inner tooth of the sliding sleeve. Not until reaching the synchronous rotational speed can the sliding sleeve be inserted in the outer tooth of the clutch body past the blocking surfaces of the synchronizer ring.
When upshifting the transmission, that is, when introducing a higher gear, the gearwheel coaxial with the sliding sleeve to which the connection is produced upon upshifting rotates at first quicker than the sliding sleeve so that it usually has to be decelerated to reach a synchronous speed via the synchronizer ring. But if strong braking forces appear upon the transmission, for example, as consequence of the higher viscosity of the transmission oil when the transmission is cold, the wheel set is retarded by the braking forces after disengagement of the lower gear whereby the rotational speed of the transmission during engagement of the higher gear can drop to a point where synchronous speed results between the sliding sleeve and the clutch body, and the sliding sleeve slides past the locking surfaces on the synchronizer ring without frictional-engagement connection being produced between the synchronizer ring and the clutch body. Due to this braking effect and further reduction of the rotational speed of the gearwheel coaxial with the sliding sleeve, it is possible to arrive at a so-called cold rasping which is felt as disagreeable.
To prevent said unpleasant noise, German Patent 34 44 670 describes a synchronizing device for gear clutches of selector transmissions for motor vehicles having at least one wheel pair whose gearwheel coaxial with the sliding sleeve non-rotatably connected with a shaft via a synchronizer body and having an inner tooth can be switched in and off the power flow, the same as having a synchronizer ring which in peripheral direction has a form-locking connection with the sliding sleeve and a frictional-engagement connection with the clutch body and which has blocking surfaces for the sliding sleeve which upon each relative rotation between clutch body and sliding sleeve prevent in the end positions defined by the form-locking connection between synchronizer ring and sliding sleeve an engagement of the inner tooth of the sliding sleeve in the outer tooth of the clutch body and allow it only when reaching the synchronous rotational speed during rotation of synchronizer ring and clutch body. The in moving direction forward blocking surfaces on the sliding sleeve have here a larger axial extension than the in moving direction rear blocking surfaces. The outer tooth of the clutch body, the same as the blocking surfaces of the sliding sleeve, are asymmetrically designed but in a manner such that even though having the same inclination relative to the axial direction are offset in relation to the longitudinal center of each tooth so that the two treads belonging to one tooth have different axial extensions and thus surfaces of different size, the in moving direction forward blocking surfaces on the sliding sleeve having the larger axial extension compared with that of the in moving direction rear blocking surface.
By using a defined asymmetry in the ridge of the blocking tooth of the sliding sleeve, there is purposefully reinforced the effect that in an upshift after end of the synchronizing operation, the synchronizer ring enters in the downshift blocking position before the sliding sleeve with its downshift blocking edge has run past the downshift blocking edge of the synchronizer ring. The downshift blocking position is the position on the opposite rotation stop while the downshift blocking surface is the long one of the blocking surfaces on the sliding sleeve. After unblocking from said downshift blocking position, the shifting operation can be terminated without rasping engagement. However, as result of the above described asymmetry, there occurs on the sliding sleeve after an upshift, while the synchronizer ring enters in the downshift blocking position, a power pulse clearly to be felt as impact on the shifting lever.
The problem on which the invention is based is to prevent the power pulse on the sliding sleeve, thus preventing the impact acting upon the shift lever.
The invention proposes for gear clutches, specially of selector transmissions for motor vehicles, a synchronizing device having at least one pair of wheels of which the gearwheel coaxial with a sliding sleeve has a clutch body with outer tooth and by axial movement of the sliding sleeve, non-rotatably connected with a shaft via a synchronizer body and having an inner tooth, can be switched in and off the power flow. The synchronizing device has in addition a synchronizer ring which in axial direction has a form-locking connection with the sliding sleeve and a frictional-engagement connection with the clutch body and which has blocking surfaces for the sliding sleeve which prevent in the end positions defined by the form-locking connection between synchronizer ring and sliding sleeve an engagement of the inner tooth of the sliding sleeve with the outer tooth of the clutch body and allow the engagement only when the synchronous rotational speed is reached during rotation of synchronizer ring and clutch body. The in moving direction forward blocking surfaces on the tooth of the sliding sleeve have a smaller extension than the in moving direction rear blocking surfaces. In the invention an asymmetry is defined in the ridge of the blocking tooth of the sliding sleeve which is designed contrary to the tooth mounted according to the prior art. The effect thus obtained is to prevent the entering in the downshift blocking position and to eliminate a clear power surge on the shift lever. The downshift blocking surface constitutes the short blocking surface in axial direction on the sliding sleeve. These facts apply both to the assembly of the synchronizing device on the main shaft or transmission output shaft when the forward blocking surface is in moving direction wherein the sliding sleeve, the synchronizer ring and the synchronizer body have a constant rotational speed and the rotational speed of the loose gearwheel is synchronized, and to the assembly of the synchronizing device upon the countershaft in which the rotational speed of the loose gearwheel is constant and the rotational speed of sliding sleeve, synchronizer ring and synchronizer body is synchronized when the rear blocking surface is in moving direction.